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Field  Columbian  Museum. 

Publication   no. 

Geological  Series.  Vol.  II,  No.  7. 


THE  CARAPACE  AND  PLASTRON 

OF  BASILEMYS  SINUOSUS, 

A  NEW  FOSSIL  TORTOISE  FROM  THE 
LARAMIE  BEDS  OF  MONTANA. 


BY 


Elmer  S.  Riggs, 

Assistant  Curator,  Division  of  Paleontology. 


Oliver  Cummings  Farrington,   Ph.  D. 

Curator  of  (leology. 


CO 


Chicago,  U.  S.  A. 
F'ebruary  1,  1906. 


THE  CARAPACE  AND  PLASTRON  OF  BASILEMYS  SINUOSUS, 

A  NEW  FOSSIL  TORTOISE  FROM  THE  LARAMIE 

BEDS  OF  MONTANA. 


BY  E.  S.  RIGGS. 

An  unusually  well-preserved  shell  of  a  tortoise  (P.  12008)  col- 
lected by  the  Museum  Expedition  of  1904  presents  new  and  inter- 
esting characters.  The  specimen  is  evidently  closely  related  to  a  form 
described*  by  Cope  from  the  Judith  River  Beds  of  Montana  as  Comp- 
semys  variolosus.  This,  with  a  more  complete  specimen  from  the 
Belly  River  series  of  Alberta,  was  later  referred!  by  Lambe  to  the 
genus  Adocus,  and  filially  by  Hay  to  a  proposed  new  genus,  Basilemys% 
The  size  of  the  specimen  under  consideration  is  almost  identical 
with  that  described  by  Lambe  and  the  dermal  markings  are  very 
similar,  but  it  differs  notably  in  the  form  of  the  anterior  end  of  the 
plastron  and  the  arrangement  of  gular  shields.  The  median  sulcus 
of  the  plastron  is  remarkably  sinuous,  crossing  and  recrossing  the 
median  line  and  often  deviating  widely  from  it.  On  account  of  this 
character  the  specific  name  sinuosus  is  proposed  for  it.  It  is  provi- 
sionally referred  to  Basilemys  pending  the  definition  of  that  genus. 

The  specific  characters  are  as  follows:  Anterior  end  of  plastron 
produced  into  a  thick  rounded  knob;  gular  shields  long  and  narrow 
and  meet  at  the  median  line;  median  sulcus  unusually  sinuous. 

The  specimen  as  a  whole  is  in  a  fine  state  of  preservation.  It 
was  found  in  a  bed  of  hard  but  uncemented  sand  containing  bones 
of  Triceratops,  Trachodon,  and  other  characteristic  Laramie  fossils. 
The  shell  was  lying  on  the  plastron  in  its  normal  position.  It  has 
been  somewhat  flattened  by  compressure  in  the  vertical  direction. 
The  carapace  is  complete  with  the  exception  of  a  few  fragments  miss- 
ing from  the  vertebral  region  and  a  section  from  the  right  side,  in- 
cluding the  posterior  half  of  the  second  and  the  anterior  half  of  the 
third  pleural  plates,  together  with  the  greater  part  of  the  fifth  and 
the  anterior  part  of  the  sixth  peripheral  plates.  Much  of  the  con- 
tact between  the  carapace  and  plastron  is  also  lost.  The  remainder 
of  the  plastron  is  preserved  entire.  However,  the  inferior  surface 
is  modified  by  compressure  so  as  to  be  deeply  concave. 

•Pro.  Acad.  Nat.  Sci.  Phila.  1876,  p.  957. 
fThe  Ottawa  Naturalist,  Vol.  XVI.  p.  63. 
tNomen  Nudem,  Bull.  U.  S.  Geol.  Surv.  Nov.  179,  p.  445. 

249  • 


250  Pibld  Columbian  Museum — Geology,  Vol.  III. 

The  shell  is  in  general  structure  broad  and  low,  flat  and  emargi- 
nate  at  the  interior  end,  but  steep  posteriorly.  The  carapace  and 
plastron  are  firmly  united  by  a  wide  bridge  which  extends  more  than 
half  the  entire  length  of  the  shell.  The  whole  of  the  free  surface  is 
marked  by  pittings  which  vary  in  depth,  structure,  and  arrangement 
in  different  parts  of  the  shell.  The  horny  shields  are  outlined  by 
narrow  sulci  which  are  plainly  marked  in  the  vertebro-costal  region, 
and  in  the  plastron,  though  less  conspicuous  between  the  marginals. 
The  sutures  joining  the  bony  plates  are  everywhere  closed,  so  that 
in  some  places  they  cannot  be  traced  by  the  aid  of  a  lens.  The  centra 
of  the  dorsal  vertebrae  have  been  detached  and  lost  from  the  speci- 
men entirely.  The  neural  plates  bear  on  their  inferior  surfaces  an 
interrupted  median  ridge  indicating  the  attachment  of  the  neural 
spines.  The  proximal  ends  of  the  pleural  plates  bear  stout  tuber- 
cular processes  for  vertebral  attachment.     Plate  LXXVII. 

The  carapace  is  relatively  thin  throughout.  The  anterior  end 
is  unusually  flat,  a  character  which  has  evidently  been  accentuated 
by  compressure  in  fossilization.  The  nuchal  border  is  rounded  and 
indented  by  a  wide  concavity.  Elsewhere  the  free  margin  is  drawn 
to  a  sharp  angle.  The  posterior  end  is  markedly  convex  in  the  pygal 
region.  The  margin  is  slightly  recurved  over  the  femora,  but  uni- 
formly convex  and  overhanging  at  the  median  line.     Plate  LXXVII. 

The  neural  plates  are  irregularly  hexagonal,  but  vary  in  size  and 
in  outline.  A  certain  amount  of  asymmetry  is  also  noticeable  in 
them.  The  first  is  broadly  coffin-shaped,  with  the  large  end  directed 
backward.  It  articulates  laterally  with  the  first  pair  of  pleurals, 
postero-laterally  with  v  the  second  pair,  and  posteriorly  by  a  concave 
line  with  the  second  pleural.  The  second  is  sub-ovate  in  outline 
and  notably  smaller  than  the  first.  Its  pleural  articulation  is  con- 
fined to  the  second  pair.  The  third  neural  is  a  trifle  smaller  than 
the  first  and  has  an  outline  similar  but  reversed  in  position.  Thus 
it  articulates  antero -laterally  with  the  second  pair  of  pleurals  and 
laterally  with  the  third  pair.  The  entire  fourth  and  part  of  the  fifth 
are  missing  from  this  specimen.  They  were  evidently  narrower  than 
the  third  but  similar  in  form.  The  sixth  is  notably  asymmetrical. 
The  anterior  end  and  right  side  have  the  usual  form,  but  the  left 
side  is  elongate  so  as  to  articulate  with  the  whole  mesial  end  of  pleural 
vi  and  postero-laterally  by  a  short  line  with  pleural  vn.  The 
seventh  neural  is  thus  excluded  from  its  normal  articulation  on  the 
left  with  pleural  vn,  and  is  correspondingly  asymmetrical.  It  is 
also  much  smaller.     The  eighth  neural  is  much  shortened  antero- 


Feb.,  1906.     Carapace  and  Plastron  of  Basilemys  Sinuosus.       251 

posteriorly  and  lies  opposite  the  suture  between  pleurals  vn  and 
viii.  A  ninth  irregularly  rounded  plate  intercolated  between  the 
last  pair  of  costals  may  be  regarded  as  a  post-neural. 

The  pleural  plates  extend  only  about  two-thirds  of  the  distance 
from  the  neural  suture  to  the  margin  of  the  carapace.  Their  articu- 
lation with  the  neurals  has  been  described  in  the  preceding  para- 
graph. Distally  they  articulate  with  the  marginals,  breaking  joints 
in  a  mosaic  pattern.  Pleurals  1  to  111  inclusive  are  directed  obliquely 
forward.  Pleural  iv  stands  at  a  right  angle  to  the  median  line. 
From  this  point  the  remainder  of  the  series  becomes  more  and  more 
directed  obliquely  backward  until  the  last  pair  conforms  to  the  wide 
A-shape  of  the  first  pygal.  Pleural  1  is  much  the  broadest  of  the 
series,  articulating  anteriorly  with  the  nuchal  and  peripherals  one 
and  two.  Distally  it  abuts  the  whole  mesial  border  of  peripheral 
three  and  a  small  anterior  portion  of  four.  Pleural  11  is  long  and 
narrow,  meeting  only  two-thirds  of  peripheral  four.  Pleural  in  is 
widest  at  the  distal  end,  articulating  antero-laterally  with  the  fourth 
and  laterally  with  the  fifth  peripheral.  Pleural  iv  is  uniform  in 
width,  and  has  a  distal  articulation  similar  to  the  perceding.  Pleural 
v  is  slightly  expanded  toward  the  extremity  and  presents  an  almost 
equal  surface  to  marginals  six  and  seven.  The  suture  between  Pleu- 
rals v  and  vi  is  unusually  sinuous.  The  latter  element  is  noticeably 
narrower  and  has  its  distal  articulation  similar  to  the  preceding. 
Pleural  vn  is  shorter,  and  much  narrower  at  the  mesial  end.  It 
articulates  distally  with  peripheral  eight  by  a  short  suture,  but  chiefly 
with  nine.  Pleural  vni  is  shortest  and  smallest  of  the  series.  It 
arises  from  the  eighth  and  ninth  neurals,  and  is  more  uniform  in 
width  than  the  preceding.  It  meets  peripheral  nine  in  a  short 
antero-lateral  suture  as  well  as  half  the  mesial  surface  of  peripheral 
ten. 

The  first  pygal  plate  has  the  form  of  a  wide  A.  Its  lateral  wings 
are  co-extensive  with  the  last  pair  of  pleurals,  with  which  they  articu- 
late anteriorly.  Laterally  they  abut  a  third  of  the  mesial  surface 
of  peripheral  ten.  The  posterior  surface  is  concave  to  receive  the 
rounded  surface  of  the  succeeding  element.  The  second  pygal  is  a 
wide  irregular  figure,  convex  on  the  anterior  surface  and  bounded 
by  three  concave  facets  posteriorly.  These  facets  articulate  with 
the  eleventh  pair  of  peripherals  and  the  third  pygal.  Laterally  this 
bone  also  presents  a  small  pair  of  surfaces  to  the  postero -lateral  faces 
of  the  tenth  pair  of  peripherals.  The  third  pygal  is  not  more 
than  half  as  large  as  the  second  and  is  sub-hexagonal  in  outline. 


252  Field  Columbian  Museum — Geology,  Vol.  III. 

The  peripherals  are  eleven  in  number  exclusive  of  the  nuchals 
and  last  pygal.  The  series  as  a  whole  is  unusually  deep,  especially 
in  the  lateral  region  where  the  plates  above  the  angle  of  the  cara- 
pace .are  more  than  half  the  length  of  the  adjacent  pleurals.  Only 
the  last  pair  is  covered  entirely  by  the  marginal  shields.  The  nuchal 
differs  from  the  common  hexagonal  type  in  that  the  anterior  border 
forms  a  reentrant  angle  at  the  median  line.  The  peripheral  bones 
gradually  increase  in  depth  from  first  to  fourth.  The  fourth,  fifth, 
and  sixth  are  similar  in  size  and  are  largest  of  the  series.  With  the 
seventh  there  is  a  decided  reduction  in  antero-posterior  diameter. 
The  ninth  and  tenth  diminish  rapidly  in  length,  the  eleventh  is  much 
the  smallest  of  the  series.  The  tenth  presents  an  equal  surface  to 
articulate  with  the  eighth  pleural  and  the  first  two  pygals.  Peri- 
pherals three  to  seven  inclusive  form  the  bridge. 

The  vertebral  shields  are  notably  variable  in  outline.  The  first 
has  the  form  of  an  irregular  truncated  pyramid  with  its  base  at  the 
anterior  marginal  suture.  In  this  specimen  it  is  quite  asymmetrical. 
The  second,  third  and  fourth  are  much  longer  than  wide.  The  sec- 
ond and  third  are  sub -rectangular  in  outline  and  nearly  equal  in  size. 
The  fourth  is  somewhat  smaller,  narrower  at  the  posterior  end  and 
more  irregular  in  outline.  The  fifth  is  the  largest  of  the  series.  It 
has  the  form  of  a  wide  triangle  whose  base  is  at  the  posterior  mar- 
ginal suture. 

The  costal  shields  are  four  in  number.  The  first  has  the  form 
of  a  quadrant  of  a  circle  whose  center  is  at  the  mid-lateral  border 
of  vertebral  II.  It  overlies  the  greater  part  of  the  first  and  half  of 
the  second  pleural,  as  well  as  parts  of  the  first  four  peripheral  bones. 
The  second  and  third  costals  are  rectangular  in  outline.  The  second 
is  somewhat  broadest  in  its  antero-posterior  diameter  and  extends 
over  the  posterior  half  of  the  second,  all  of  the  third  and  the  anterior 
half  of  the  fourth  pleural  plates,  as  well  as  parts  of  the  fourth,  fifth 
and  sixth  peripherals.  The  third  costal  shield  bears  a  similar  rela- 
tion to  the  fourth,  fifth  and  sixth  pleurals,  and  the  sixth,  seventh  and 
eighth  peripherals.  The  fourth  costal  shield  is  an  irregular  quadri- 
lateral and  is  the  smallest  of  the  series.  Its  relation  to  the  neural  and 
peripheral  plates  is  similar  to  that  of  the  second  and  third.  The 
intercostal  sulci  have  the  usual  position  opposite  the  middle  of  the 
vertebral  shields. 

The  marginal  shields  are  twenty-five  in  all.  The  sulcus  separa- 
ting them  from  the  vertebrals  and  costals  falls  far  without  the  pleuro- 
peripheral  suture  and  is  little  more  plainly  marked  than  those  in  the 


Feb.,  1906.     Carapace  and  Plastron  of  Basilemys  Sinuosus.       253 

vertebral  region.  The  nuchal  shield  is  very  small.  It  is  narrow 
in  its  superior  aspect  but  rapidly  widens  as  it  rounds  the  anterior 
margin.  The  first  pair  of  marginals  are  long  and  narrow;  the  sec- 
ond and  third  increase  regularly  in  breadth.  The  fourth  to  seventh, 
inclusive,  overlie  the  bridge.  Their  distal  articulation  will  be 
described  with  the  plastron.  The  eighth,  ninth  and  tenth  diminish 
slightly  in  depth  in  the  order  named.  The  eleventh  increases  rapidly 
in  depth  toward  the  mesial  border.  The  pygal  is  deepest  of  the  series 
and  is  paired. 

The  plastron  is  suggestive  of  great  rigidity  and  strength  as  in- 
dicated by  the  wide  bridges  with  thickened  buttresses  and  firmly 
interlocking  sutures,  the  massive  anterior  process  formed  by  the 
epiplastra,  and  the  thickened  and  rugose  borders.  The  pittings  are 
more  deeply  marked  than  on  the  carapace,  and  the  arrangement  of 
shields  is  unusually  complicated.  In  its  entire  length  the  median 
sulcus  crosses  the  median  suture  fourteen  times.  At  no  point  does 
it  coincide  with  the  median  suture.  Compared  with  the  plastron 
of  B.  variolosus  as  figured  by  Lambe*  there  is  a  great  similarity. 
However,  the  epiplastrals  in  this  form  are  more  produced,  the  ento- 
plastron  noticeably  larger,  the  gular  shields  meet  at  the  median  line, 
and  the  median  sulcus  is  much  more  sinuous.      Plate  LXXVIII. 

The  epiplastra  unite  at  the  median  suture  to  form  a  thick  and 
rounded  knob,  which  may  be  termed  the  gular  eminence.  The  dis- 
tal ends  appear  on  the  inferior  surface  as  a  pair  of  wing-like  processes 
which  are  directed  postero-laterally.  The  entoplastron  is  sub- 
hexagonal  in  outline  and  one-third  broader  than  long.  Its  anterior 
margin  joins  the  epiplastra  in  two  approximately  straight  lines  which 
meet  in  an  angle  of  sixty  degrees.  The  lateral  borders  are  short, 
the  posterior  angle  very  obtuse.  The  hypoplastra  are  somewhat 
larger  than  the  hyoplastra.  In  this  specimen  there  is  a  break  in  their 
connecting  suture  at  the  median  line.  The  former  articulate  laterally 
with  peripherals  three,  four  and  five,  and  postero-laterally  they  pre- 
sent a  short  articulating  surface  to  peripherals  six.  The  hyoplastra 
articulate  laterally  with  peripherals  six  and  seven.  The  xiphiplastra 
extend  forward  almost  to  the  femoral  notches.  On  the  superior 
surface  the  gular  eminence  terminates  in  a  single  short  median  ridge, 
and  is  flanked  by  a  pair  of  marginal  ridges  which  extend  half  way 
to  the  humeral  notches.  The  entoplastron  bears  on  a  pair  of  low 
converging  ridges  the  facets  for  articulation  with  the  precoracoids. 
The  xiphiplastra  bear  a  similar  but  larger  pair  of  facets  for  ligamentary 

•Geol.  Surv.,  Canada.  Vol.  III.  part  II,  page  39. 


254     •      Field  Columbian  Museum  —  Geology,  Vol.  III. 

union  with  the  pubic  process.  From  the  femoral  notch  to  the  median 
line  the  margin  is  elevated  to  form  a  sharp  ridge,  deeply  pitted  on 
the  free  surface. 

The  dermal  shields  of  the  plastron  are  very  complex  in  arrange- 
ment. The  intergulars  are  similar  on  the  inferior  surface  to  those 
of  B.  variolosus ,  but  superiorly  they  are  extended  to  cover  the  pro- 
truding gular  process.  Between  them  the  median  sulcus  twice  crosses 
the  median  suture.  The  gulars  are  long  and  narrow,  and  meet  at  the 
median  line.  The  humerals  are  relatively  smaller  than  in  B.  vario- 
losus. They  present  for  union  at  the  median  line  a  surface  barely 
a  half -inch  in  length.  The  pectoral  shields  as  a  pair  are  similar  in 
outline  to  those  of  the  species  cited,  though  they  extend  somewhat 
farther  backward  mesially.  Between  them  the  median  sulcus  de- 
parts from  the  median  line  in  a  series  of  meanderings  in  which  it 
crosses  the  median  suture  five  times.  In  the  abdominals  it  follows 
almost  parallel  with  the  suture  making  a  single  digression  near  the 
posterior  border.  The  abdominals  send  backward  a  pair  of  peculiar 
narrow  processes  between  the  inguinals  and  femorals  to  the  border 
of  the  femoral  notch.  The  femorals  are  sub-quadrangular  in  outline, 
extending  laterally  to  the  border  of  the  femoral  notch.  In  the  anals 
the  median  sulcus  presents  the  most  fantastic  tracery,  crossing  the 
median  suture  in  a  series  of  wide  loops,  departing  from  it,  in  one  in- 
stance, nearly  two  inches  and  finally  returning  to  it  at  the  posterior 
margin.  On  account  of  portions  missing  at  the  lateral  angle  of 
the  carapace  it  cannot  positively  be  determined  whether  the 
marginals  are  divided  into  an  inframarginal  series.  From  the  fact 
that  no  evidence  of  a  dividing  sulcus  can  be  made  out  on  either  side, 
as  well  as  the  opposite  position  of  the  vertical  sulci  on  each  side  of 
the  gap,  it  is  assumed  that  the  series  is  not  divided  into  marginals  and 
inframarginals,  respectively. 

From  the  narrow  lateral  extremities  of  the  pectorals  radiate 
three  wedge-shaped  shields.  The  anterior  and  smallest  is  the  axillary 
shield  which  overlies  the  axial  buttress  and  extends  upward  along 
the  free  margin  of  the  carapace  to  join  the  second  nuchal.  The 
other  shields  radiating  from  this  point  are  the  fourth  and  fifth 
marginals.  The  sixth  marginal  is  very  broad  at  its  ventral 
border,  joining  nearly  the  whole  lateral  surface  of  the  abdominal 
shield.  Two  pairs  of  shields  converge  at  the  postero-lateral 
angle  of  the  abdominals.  The  most  anterior  is  the  seventh  mar- 
ginal, which  narrows  mesially  almost  to  a  point.     Back  of  this  lies 

♦Proc.  Acad.  Nat.  Sci.  Phila.  1876,  p.  257. 


Feb,,  1906.     Carapace  and  Plastron  of  Basilemys  Sinuosus.      255 

the    inguinal    shield    which     overlies    the     posterior    or    inguinal 
buttress. 

The  sculpturing  of  the  shell  in  "members  of  this  genus  has  been 
variously  described.  In  his  original  description*  of  the  type  species 
B.  variolosus  Cope  described  the  dermal  markings  as  follows:  "The 
sculpture  consists  of  round  fossae,  which  are  deeply  impressed,  and 
are  arranged  quincuncially,  so  that  their  borders  never  form  straight 
lines.  The  latter  are  also  more  or  less  angulate  on  the  edges,  so  that 
the  surface  has  a  more  than  usually  rugose  character."  Of  the  species 
B.  (Compsemys)  imbricarius  he  writes  as  follows:*  "The  character 
of  this  sculpture  distinguishes  the  species  and,  in  the  present  instance, 
in  a  special  manner.  It  consists  in  the  C.  imbricarius  of  excavations 
bounded  on  the  sides  by  a  short  ridge  each,  which  alternate  with  each 
other.  Thus  each  bounding  ridge  terminates  abruptly  at  the  fundus 
of  one  of  the  fossae,  while  the  other  end  of  the  fossa  rises  and  con- 
tracts to  another  ridge."  In  the  more  complete  specimen  described 
by  Lambe  as  belonging  to  Adocus  variolosus  the  markings  are  de- 
scribed as  follows :f  "The  sculpture  consists,  when  most  rugose, 
of  well-excavated  pits  of  rounded  hexagonal  outline  arranged  quin- 
cuncially; the  dividing  ridges  are  angular  and  narrower  than  the  pits 
are  wide,  their  angularity  and  height  being  more  pronounced  at  the 
junction  of  every  three  pits  with  each  other." 

It  will  be  noted  that  the  quotations  from  Cope's  description  of 
B.  imbricarius  and  Lambe's  characterization  of  the  sculpture  in  B. 
variolosus  describe  very  similar  markings.  Moreover,  the  various 
types  of  markings  indicated  by  these  three  descriptions  are  all  to  be 
found  in  various  parts  of  the  specimen  under  consideration.  In 
fact,  the  sculpture  in  various  regions  of  carapace  and  plastron  varies 
so  widely  that  no  area  could  be  taken  as  typical  with  the  assurance 
that  fragments  from  other  parts  of  the  shell  could  be  recognized  from  it. 

The  pittings  are  most  conspicuous  and  most  regular  on  the  plas- 
tron and  about  the  margin  of  the  carapace.  In  the  vertebral  region 
they  are  least  conspicuous  and  without  any  regular  arrangement. 
On  the  superior  surface  of  the  gular  process  and  the  anterior  half  of 
the  femoral  shields  there  is  to  be  found  the  type  of  sculpture  described 
in  B.  imbricarius  in  which  a  sharp  ridge  terminates  abruptly  at  the 
fundus  of  the  succeeding  pit.  It  is  noticeable,  however,  that  in  those 
portions  of  the  femoral  shields  which  overlie  the  xiphiplastra  the 
arrangement  suddenly  changes  to  a  series  of  irregular  diagonal  rows. 


•Ibid. 

tGeol.  Surv.  Canada.  Vol.  Ill,  part  p.  40. 


256  Field  Columbian  Museum — Geology,    Vol.  III. 

Similarly  on  the  lateral  surface  of  the  gular  process  the  markings 
fall  into  straight  rows  in  which  the  pits  of  adjacent  rows  alternate 
so  as  to  form  diagonal  lines.  Thus  the  pits  are  in  regular  rosettes  — 
patterns  of  six  around  one.  In  other  parts  of  the  plastron  may  be 
occasionally  recognized  groups  of  fives,  of  fours  and  of  threes,  but 
for  the  most  part  no  regular  arrangement  is  to  be  recognized. 

It  is,  therefore,  probable  that  if  the  whole  carapace  and  plas- 
tron of  B.  variolosus  and  B.  imbricatus  were  known  the  same  regional 
variation  would  be  found  to  obtain.  At  all  events,  little  reliance 
can  be  placed  upon  the  depth  or  arrangement  of  pittings  as  bases 
for  specific  determination  in  this  genus. 

MEASUREMENTS. 

M 

Length  of  carapace  at  median  line 705 

Breadth  of  carapace 565 

Length  of  plastron 650 

Breadth   of  hypoplastra 480 

Length  of  bridge 360 

Greatest  breadth  of  nuchal   plate 145 

Least  breadth  of  nuchal  shield 007 

Greatest  breadth  of  first  pleural  plate 112 

Greatest  length  of  third   pleural  plate 205 

Greatest  breadth  of  anterior  pygal .1 70 

Breadth  of  entoplastron 148 

Thickness  of  epiplastra  at  gular  eminence 060 


•■'USEUM. 


:v.  i; 


Pen.  I 


PI.  I 


COi.  I. 


m 


BASILEMYS     SINUOSUS,  ,  : 


Nu    nuchal  plate.  Py.  L  to  3,  pygal  plates. 

N.  1  to  8,  neural  plates.  V.  I  to  V,  vertebral  shields. 


P.  N.,  post-neural  plate. 
Per.  1  to  11,  peripheral  plates 


Cos.  I  to  IV,  costal  shields. 
M.  I  to  XII,  marginal  shields. 


,ii\-       teueouMie   8YM3jieA8 


.?btairia  Ifiicfemv  ,V  oJ  I  .V 

.ablaiifa  IsJaoD  ,VI  oJ  I  .acG 

.abhiiia  Isahnsai  ,IIZ  a)  1  .M 


.alfilq  Isrfoun  ,.uH 

.aaifila  Isiuaa  ,8  oJ  I  M 

.9tslq  kiuen-Jaoq  ,.VI  .4 

.asluiq  Imarfqhaq  ,11  oJ  1 .134 


FIELD  COLUMBIAN   MUSEUM. 


GEOLOGY,  VOL.  II.     PLATE  LXXVI. 


Carapace  of  Basilemys  sinuosus.  dorsal  view,  X  %i. 


ILUMBIAK   M. 


BASILEMY8     8INU08U8,    X    %,. 


Ep.,  e  pi  plastron. 
Ent.,  entoplastron. 
Hyo.,  Hyoplastron. 
Hyp.,  Hypoplastron. 
Xiph.,  xiphoplastron. 
I.  G.,  intergular  shield. 
G.,  gular  shield. 


Ing.,  inguinal  shield. 


H.,  humeral  shield. 

Pec,  pectoral  shield. 

Ab.,  abdominal  shield. 

Fem.,  femoral  shield. 

An.,  anal  shield. 

Ax.,  axial  shield. 

M.  IV  to  VII,  marginal  thield. 


.it*    x    ,eU80UKllti     8YM3Jl8AtJ 


.bbids  lsismod  ,.H 

.btaidg  IfiioJDaq  ,.094 

.bbids  Isnimobcls  ,.dA 

.bbids  isioorel  ..aisT 

.bbide  Isns  t.nA 

.bbirfa  Isixs  ,.xA 

.bbidt  bfli§nsm  ,11 V  ol  VI  M 


.bbide  lsaiujjfli  ,.§ni 


.iKnJ8fiiqiq3  ,.q3 

.notJesIqolria  ,.Jn3 

.noiJaslqoyH  ..o^H 

.noiJasIqoqYH  ,.q^H 

.noilaslqoiiqix  ,.dqiX 

.bbida  iBlujmlni  ,.0  .1 

.bbide  islus  ..O 


FIELD  COLUMBIAN   MUSEUM. 


GEOLOGY,  VOL.  II.     PLATE  LXXVII. 


Shell  of  Basilemys  sinuosus,  ventral  view,  x  -ii. 


FIELD  COLUMBIAN    MUSEUM. 


GEOLOGY,  VOL.  II.     PLATE  LXXVIII. 


Plastron  of  Basilemys  sinuosus.  visceral  surface,  X  -\^. 


a 


